I do like this camera, but it seems overpriced at $600. For that money, I can buy a much more versatile used Olympus E-PL1s ($375, add housing about $500). After you add a housing and strobes, does it really have a size advantage? I guess I'm just being a contrarian, trying to resist another incursion to my bank account.
Humm, huge diffences, but as already posted, expect the street price to be similar to the other camera's in that group.. or around $400 (or about the same as a used E-PL1, but with a far better lens).
As the case would be cheaper for the XZ-1, it would actually be a total lower cost.
However, there are a huge number of differences here, and most favor the XZ-1:
1. Interchangeable lens cameras typically come with a short range zoom. It does not focus close, it has less depth of field and the range is usually way to limited.
2. Image quality is not that much different, although the pen series should have a better dynamic range, which normally is not an issue underwater.
3. The XZ-1 will have advantages in macro, zoom range and depth of field, and as long as one is shooting with a flat port, should be a far more usable camera.
4. Add a dome port and and a wide angle lens to the pen and you can take amazing images. If, however, you dive in less than clear water (like I normally do), that is not very useful. But doing that will more than double the cost.
5. You can add a wide angle wet lens to the XZ-1, but the image quality will never be as good.
So if you only dive in clear water, like wide angle images, and you can afford a couple of thousand, then get the pen...if you want to take a large variety of images, and/or on a budget, then the XZ-1 will be a better deal.